Little is known about the short-term consequences of persistent H. pylori infection in apparently healthy children. Short-term consequences such as impacts on growth, nutritional status and susceptibility to co-infections may influence overall health status throughout life as well as risk of cancer and other chronic disease in adulthood. Such short-term consequences can be examined in a community intervention approach that begins with two comparable populations of H. pylori-infected children, eliminates the infection in one of the populations and follows both groups over time to observe differences between children whose infection persists and those who remain uninfected. The proposed study will undertake such an intervention in two rural communities in the Andean region of Narino, Colombia, where H.pylori infection is nearly universal by adolescence and gastric cancer rates are among the highest in the world. The design of this study will also facilitate secondary aims of identifying factors that predict successful elimination of infection in a high prevalence population, as well as identifying determinates of persistence and reinfection. Another secondary aim will be to study the histopathologic features of H.pylori infection in pediatric gastroenterology patients form this geographic region. Accessibility to biopsies form such patients will also permit validation of diagnostic cutoff values for noninvasive H. pylori detection methods in our study population. In addition, we will pursue supplemental studies to evaluate methods for obtaining bacterial specimens form the community-based population of children in order to investigate the role of strain differences in the shortterm consequences of infection. The major specific aim of this study are: 1) To conduct a community intervention in two rural Andean populations (children in the Narino-Genoy community will be maintained clear of H.pylori infection with anti-H.pylori therapy and monitored for H.pylori status and selected health indicators during a period of four years; children in the La Laguna-Cabrera community will receive no anti-H.pylori therapy and will be monitored for H.pylori status and selected health indicators during a period of four years); 2) To compare anthropometric health-status indicators in children with persistent H.pylori infection and those who remain free of H.pylori infection; 3) To compare hematocrit levels in children with persistent H.pylori infection and those who remain free of H.pylori infection; 4)To compare the incidence of diarrheal disease in children with persistent H.pylori infection and those who remain free of H.pylori infection; 5) To compare the occurrence of the following coinfections in children with persistent H.pylori infection and those who remain free of H.pylori infection: ova and parasites (in particular, Giardia lamblia, Entamoeba histolytica and Ascaris lumbricoides); 6) To investigate whether the presence of co-infections modifies the effect of H.pylori persistence on general health status and diarrheal disease. In addition the proposed study has the following secondary aims; 1) To identify predictors of successful elimination of H.pylori infection in children from a high prevalence population as well as determinants of persistence and reinfection; 2) To describe the histopathologic features of H.pylori infection in pediatric gastroenterology patients from this geographic region; 3) To assess the accuracy of noninvasive diagnostic methods for H.pylori infection (urea breath test; stool antigen test) against biopsy-based diagnosis in the local pediatric population.